Epoxidation process

ABSTRACT

DRAWING   1. IN THE CONTINUOUS PROCESS FOR THE PREPARATION OF PROPLENE OXIDE BY THE REACTION BETWEEN PROPYLENE AND AN ORGANIC HYDROPEROXIIDE IN THE PRESENCE OF A LIQUID PHASE REACTION MEDIUM AND IN THE PRESENCE OF A CATALYST SELECTED FROM AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF TITANIUM, VANADIUM, CHROMIUM, COLUMBIUM, SELENIUM, ZIRCONIUM, MOLYBDENUM, TELLURIUM, TANTALUM, TUNGSTEN, RHENIUM AND URANIUM; THE IMPROVEMENT WHICH COMPRISES, CONTINUOUSLY CONDUCTING THE REACTION IN A REACTOR AT A TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 90* C. AND ABOUT 200* C. AND AT THE AUTOGENOUS PRESSURE OF THE LIQUID PHASE REACTION MEDIUM SO THAT SAID MEDIUM IS A BOILING LIQUID, THE REACTOR FEED COMPRISING 10 TO 80 MOL PERCENT PROPYLENE AND 1 TO 60 MOL PERCENT HYDROPEROXIDE, CONTINUOUSLY VOLATILIZING A PORTION OF THE LIQUID PHASE REACTION MEDIUM DURING THE CONDUCT OF THE REACTION, AS A RESULT OF SAID BOILING, SAID VOLATILIZED PORTION CONTAINING AT LEAST ONE-FOURTH OF THE PROPYLENE OXIDE CONTAINING VA , REACTION, WITHDRAWING THE PROPYLENE OXIDE CONTAINING VAPROIZED REACTION MEDIUM FROM THE REACTOR AS A VAPOT, CONTINUOUSLY WITHDRAWING THE UNVAPORIZED REACTION MEDIUM CONTAINING THE BALANCE OF THE PROPYLENE OXIDE PRODUCT FROM THE REACTOR AS A LIQUID, CONTINUOUSLY SEPARATING PROLYLENE OXIDE FROM SAID WITHDRAWING VAPORIZED REACTION MEDIUM BY FRACTIONAL DISTILLATION AT TEMPERATURES NOR TO EXCEED 160* C. AND CONTINUOUSLY RECYCLING PROPYLENE IN SAID WITHDRAWN VAPORIZED REACTION MEDIUN TO THE EPOXIDATION REACTION AS PART OF THIS FEED THERETO.

Nov. 19, 1974 T. w. sTElN ETAL 3.849.451

EPOXIDATION PROCESS rginal Filed June 30, 1970 /NVENTORS 771'E0D0/2E WSTE/N HAROLD G/LMAN R/CHARD L. BOBECK H7-LEV United States Patent3,849,451 EPOXIDATION PRQCESS Theodore W. Stein,Hastings-on-the-I-iudson, Harold Gilman, Milwood, and Richard L. Bobeck,East Northport, N.Y., assignors to Halcon International, Inc.Continuation of abandoned application Ser. No. 51,332, June 30, 1970.This application Dec. 4, 1972, Ser. No.

Int. Cl. C07d l 08 U.S. Cl. 260-348.5 L 3 Claims ABSTRACT 0F THEDISCLOSURE BACKGROUND In recently issued Belgian patents, Nos. 663,859,665,082 and 644,090, there is disclosed a process for the epoxidation ofolefins in the presence of catalytically effective amounts of metals.The process disclosed in these Belgian patents is capable of producingepoxides from the olefinic starting materials in high yields7 i.e., withonly small amounts of undesired side products. The catalysts are one ormore metals selected from the group consisting of titanium, vanadium,chromium, columbium, selenium, zirconium, niobium, molybdenum,tellurium, tantalum, tungsten, rhenium and uranium. 0f the foregoing,vanadium, tungsten, molybdenum, titanium and selenium are the preferredspecies. The catalyst metals can be employed in conjunction withalkaline (or basic) substances such as alkali metal compounds oralkaline earth metal compounds.

This is a continuation of application Ser. No. 51,332 filed June 30,1970, and now abandoned.

The catalyst metals are preferably supplied to the reaction either inthe finely divided metallic state or in the form of their compounds.Organo-metallic compounds of the above metals in such forms as, forexample, naphthenates, stearates, octanoates, chelates, associationcompounds and enol salts (eg. as acetoacetonates) as well as in the formof alkoxy compounds, are useful. Inorganic forms such as, for example,the oxides (c g., in the case of molybdenum, M0203, M002 and M003) acids(e.g., molybdic acid) chlorides, oxychlorides, fluorides, bromides,phosphates, sulides, heteropoly acids (e.g., phosphomolybdic acid andalkali metal salts thereof) and the like are also useful. 4Effectiveamounts of these catalysts desirably are suicient to provide at least0.00001 mcl of metal per mol of organic hydroperoxide present in thereaction. Amounts of metal as great as 0.1 mol per mol of organichydroperoxide or even more can be employed.

As disclosed in the hereinabove cited Belgian patents, during theepoxidation reaction the olefin is epoxidized to form the correspondingoxirane derivative and the organic hydroperoxide is converted to thecorresponding alcohol. Desirable reaction conditions include a reactiontemperature between about 0 C. and about 200 C., a reaction pressuresufficient to maintain a liquid phase, a molar ratio of olefin toorganic hydroperoxide in the reaction between about 1:1 and about 20:1,and reaction times normally between about ten minutes and about tenhours.

SUMMARY oF THE INVENTION The hereinabove described reaction is highlyexothermic (approximately 60,000 calories of heat are liberated per grammol of epoxide formed in the primary reaction). This heat of reaction isdesirably removed from the reactor substantially as fast as it isliberated and it is an advantage of our invention that this highlyexothermic heat of reaction is more readily removed. As a consequence,the maintenance of close reaction temperature control is facilitated andthe close temperature control achieved by the practice of our inventionresults in an improvement in process yields.

While the selectivities obtained in the epoxidation process ashereinabove described are high, some of the desired epoxide productformed in the reaction is lost, apparently in part by reaction with theorganic hydroperoxide raw material. Without intending to be limitedthereby, we believe that this reaction results in the formation ofhydroxyalkyl peroxides, i.e., `R-0--0-R-0H wherein R is the organicradical of the organic hydroperoxide and R s an organic radicalcorresponding to the olefin raw material. In a preferred embodiment ofour invention side reactions such as that postulated hereinabove areminimized with the resultant advantage of an increase in yield of thedesired epoxide product.

In accordance with our invention, we have discovered that temperaturecontrol is facilitated, resulting in improved yields, by conductingepoxidation reactions of the type hereinabove described under autogenouspressure and at a reaction temperature suicient to volatilize a portionof the liquid phase reaction medium. The phrase autogenous pressure, asused herein, means the bubble point pressure of the liquid reactionmedium at the reaction temperature. This volatilized portion of thereaction medium can be condensed and returned to the reactor, i.e., thereactor can be operated at total reux. Apart from the improved reactiontemperature control resulting from operations in accordance with thisinvention, an ancillary advantage is that the heat of reaction can beremoved in many instances by indirect heat exchange in carbon steelequipment rather than alloy steel equipment (such as stainless steel)which would otherwise be required.

However, in a particularly preferred embodiment, a significant portionof the volatilized reaction medium-"including a portion of the epoxideproduct is withdrawn from the reactor in the form of a vapor stream.This withdrawn vapor stream is then treated to recover the epoxideproduct from the other constituents of the vapor streaml volatilizedtogether with the epoxide. Materials other than the epoxide product can,if desired, be recycled to the epoxidation reactor. This particularlypreferred embodi' ment of our invention minimizes side reactions of theepoxide and, in combination with the improved temperature controlachieved by practice of our invention results in significantly improvedoverall process yields.'u

DETAILED DESCRIPTION 0E THE INW-:NTIoNl the octenes, the dodecenes.,cyclohexene,v 4vmethyl cyclohexene, butadiene, styrene,methylstyrenefvinyl toluene, vinylcyclohexene, the phenyl cyclohexenes',and the. like. IOleiins having halogen, oxygen, sulfur and the likesubstituents, including ester and ether linkages, can' beused. Suchsubstituted oleiins are illustrated by allyl alcohol,

methallyl alcohol, diallyl ether, methyl methacrylate, methyl oleate,methyl vinyl ketone, allyl chloride, and the like.

Particularly preferred olefins are propylene, n-butane-l, styrene andbutadiene. For epoxidation of these preferred oleiins, preferredcatalysts include molybdenum, titanium, vanadium and tungsten.

Organic hydroperoxides suitable for the practice of our invention havethe formula ROOH, wherein R is an organic radical, preferably asubstituted or unsubstituted alkyl, cycloalkyl, aralkyl, aralkenyl,hydroxyaralkyl, cycloalkenyl or hydroxycycloalkyl radical said organicradical having from 3-20 carbon atoms. R may also be a heterocyclicradical.

Illustrative and preferred hydroperoxides are cumene hydroperoxide,ethylbenzene hydroperoxide, tertiary butyl hydroperoxide, cyclohexanoneperoxide, tetralin hydroperoxide, methyl ethyl ketone peroxide,methylcyclohexerle hydroperoxide, andthe like, as well as thehydroperoxides of toluene, p-ethyl toluene, isobutyl-benzene,diisopropyl benzene, p-isopropyl toluene, o-xylene, m-xylene, p-xylene,phenyl cyclohexane, etc. Particularly preferred organic hydroperoxidesare ethylbenzene hydroperoxide (alpha-phenylethylhydroperoxide) tertiarybutyl hydroperoxide, and cyclohexanone peroxide.

On occasion, in the preferred embodiment of our invention wherein aportion of the vaporized reaction medium is withdrawn from the reactoras a vapor, amounts of hydroperoxide, significant in terms of yield, canbe present in the withdrawn vapor stream, either because of entrainmentor because of an appreciable partial pressure at reaction conditions orboth. The presence of appreciable amounts of such hydroperoxide in thiswithdrawn vapor stream is undesirable and such hydroperoxide isadvantageously separated from the vapor stream immediately after itswithdrawal from the reactor.

The epoxidation reaction is desirably carried out in th"l presence of asolvent. Suitable solvents are the aliphatic, naphthenic or aromatichydrocarbons or their oxygenated derivatives. Preferably, the solventhas the same carbon skeleton as the hydroperoxide used, so as tominimize or avoid solvent separation problems during product recovery.Solvent mixtures may also be employed and, indeed, commonly areemployed. Thus, for example, when ethylbenzene hydroperoxide is theepoxidizing agent employed, a particularly preferred solvent wouldcomprise a mixture of ethylbenzene and alpha-phenylethanol.

Reaction temperatures between about 0 C. and about 200 C. can beemployed in the process of our invention. In general, we desire toemploy reaction temperatures between about 90 C. and about 200 C. and weprefer to employ reaction temperatures between about 90 C. and about 150C. In each case, and essential to the practice of the present invention,the reaction is conducted under autogenous pressure. Equally essentialis that the reactor conditions be chosen to maintain a liquid phasereaction medium, as the epoxidation is a liquid phase reaction. Thus, inthe practice of the present invention, the liquid phase reaction mediumwithin the reactor is a boiling liquid. The actual reaction pressure,consequently, will be a function of the nature of the solvent, thenature of the organic hydroperoxide, and the nature of the olefin beingepoxidized. In general, the autogenous pressures of the systemsemployed, i.e., reaction pressures, will be between about atmosphericpressure and about 900 p.s.i.a. In a typical preferred embodiment,wherein propylene oxide is formed by the epoxidation of propyleneemploying ethylbenzene hydroperoxide as the epoxidant, reaction pressurebetween about 200 p.s.i.a. and about 700 p.s.i.a. will be encountered,depending upon the concentration of propylene in the reaction medium andupon the reaction temperature selected. Inerts, e.g., ethane, propane orthe like if present in the reactor can also affect reaction pressure.

In the preferred embodiment wherein the volatilized reaction medium iswithdrawn as a Vapor, the reaction temperature and reactor feedcomposition are desirably such as to permit about one-quarter or more ofthe epoxide product to be volatilized and preferably are such as topermit one-third or more of such epoxide product to be volatilized. Thiscan readily be accomplished within the temperature ranges specifiedabove. Preferably the feed to the epoxidation reactor in this preferredmode of operation comprises from about 10 to about 8O mol percent ofolefin, from about 1 to about 60 mol percent of hydroperoxide, thebalance of the feed being primarily solvent. Small amounts of othermaterials can also be present in the epoxidation reactor feed.

As hereinabove noted, the epoxidation reaction is highly exothermic.Accordingly, the vaporization of the epoxide product and other materialspresent in the reaction medium effectively consumes a substantialportion, and even in some instances all of the heat of reaction, therebypermitting close control of reactor temperature throughout theepoxidation. Where even higher degrees of vaporization of the reactionmedium (including the desired epoxide product) are sought, additionalheat can be supplied to the epoxidation reaction in known manner as, forexample, by the provision of heating coils within the reactor.Alternatively, where a lesser degree of volatilization of the reactionmedium, including the epoxide product, is sought, excess heat ofreaction can advantageously be removed in known manner as, for example,by provision of cooling coils within the epoxidation reactor.

The material volatilized during the conduct of the epoxidation reactionaccordingly comprises a portion, preferably one-third or more, of theepoxide product, a substantial amount of unreacted olefin, a portion ofthe solvent employed in the course of the reaction and a portion of thealcohol formed as a result of the utilization of the organichydroperoxide employed in the reaction (which may be identical with thesolvent). When the organic hydroperoxide have high partial pressures inthe system, the vapor stream can also contain some organichydroperoxide. This vapor stream is preferably though not essentially,withdrawn from the reactor and is treated so as to recover unreactedolefin which is advantageously recycled to the epoxidation and also torecover the volatilized epoxide product. This separation can be readilyaccomplished in known manner as, for example, by distillationtechniques. If significant amounts of organic hydroperoxide are presentin this vapor stream, we prefer that the hydroperoxide be removed priorto separation and recovery of unreacted olefin and epoxide product sinceotherwise the comparatively unstable volatilized hydroperoxide mightdecompose occasioning a loss in yield.

DESCRIPTION OF THE DRAWING The process of this invention will be morefully explained in conjunction with the attached drawing which is aschematic representation of one preferred embodiment of our invention.For purposes of illustration, but without intending any limitation uponthe scope of this invention, the feed to the process as illustrated inthe drawing is assumed to be propylene which is converted to propyleneoxide employing ethylbenzene hydroperoxide as the epoxidant. Thereaction solvent is assumed to be a mixture of ethylbenzene and alphaphenylethanol. The volatilized portion of the reaction medium is assumedto be Withdrawn from the reactor, rather than totally refluxed.

Referring to the accompanying drawing, there is provided an epoxidationreactor 10, having inlet conduit 11. Organic hydroperoxide, suitablyethylbenzene hydroperoxide and catalyst, suitably comprising molybdenume.g., in the form of the naphthenate, are supplied to reactor 10 throughconduit 12 which communicates with conduit 11 and thence to reactor 10.A suitable solvent for the reaction, e.g., a mixture of ethylbenzene andalpha phenylethanol, is also supplied to the reactor via conduit 12.Fresh propylene is supplied to reactor via conduit 13, communicatingwith conduit 11. Recycle propylene, obtained in a manner to besubsequently described is supplied via conduit 36 communicating withconduit 13.

Reactor 10 can be of the tubular type or, more suitably and as depictedin the attached drawing, can be a reaction vessel internally subdivided'by bafiies 15 into a plurality of compartments 16. Alternatively, one ormore of said compartments can be a separate reaction vessel. Thiscompartmentation of the reactor, either by internal bafiies or byprovision of several reaction vessels connected in series, provides ameans for positively preventing undesirable back-mixing of reactionproducts with the entering reactants.

Disposed within each of the compartments 16 of reactor 10 is a liquidphase reaction medium 17 comprising solvent, unreacted hydroperoxide,unreacted olefin, epoxide product, and organic alcohol formed during thereaction of the hydroperoxide with the olefin. (In many instances theorganic alcohol formed by the reaction of the hydroperoxide with theolefin is identical with the solvent.)

In accordance with this invention, the liquid phase reaction medium ismaintained under its autogenous pressure and therefore is partiallyvaporized as the reaction proceeds, i.e., the reaction is boiling. Theheat requirements for this vaporization are supplied by the heat ofreaction. This vaporized portion of the reaction medium in theembodiment depicted in the drawing is withdrawn from reactor 110 viaconduit 18 and is fed to zone 30.

In the operation of reactor 10 the reactants enter compartment 16a andaccumulate therein until the level of the liquid phase reaction mediumwithin compartment 16a exceeds the height of internal baffle (or weir)a. The liquid phase reaction medium then overflows baffle 15a and flowsinto compartment 16b. In like manner the liquid phase reaction mediumsuccessively passes into compartments 16C, 16d, and 16e, ultimatelyexiting from reactor 10 via conduit 19. The liquid reactor effluent isthen fed via conduit 19 to fractionation zone 30. If desired, therecycle propylene can be distributed into some or all compartments ofthe reactor via lines a, 40b, 40e, 40d and 40e so as to maintain aconstant concentration of propylene within each compartment by replacingthat portion which is volatilized.

The vaporized reaction medium fiows to fractionating zone 30. Infractionating zone 30 this vaporized medium and the liquid phaseepoxidation reactor efliuent, which is drawn from reactor 10 via conduit19, are processed to recover unreacted propylene and a mixturecomprising the propylene oxide product, ethylbenzene andalpha-phenylethanol solvent, and alpha phenylethanol formed as theresult of the reaction of ethylbenzene hydroperoxide with propylene.Fractionating zone 30 is preferably designed and operated to maintainthe bottoms temperatures therein at sufficiently low levels to minimizedecomposition of propylene oxide, i.e., below 160 C. and preferably ator below 130 C. The propylene so recovered is withdrawn fromfractionating zone 30 via conduit 36 and is recycled to the epoxidationreaction. The product mixture is withdrawn from fractionating zone 30via conduit 37. Facilities can be provided within fractionating zone 30for separating and purging inerts from the system to prevent theirbuild-up.

Accordingly, fractionating zone 30 functions as a depropanizationsystem. Since the design of such equipment is conventional and since thedesign and operation of such equipment is known to those skilled in theart, the equipment associated with fractionating zone 30 is not shown inthe attached drawing.

Fractionating zone 30 can often consist of two or more columns connectedin series together with the associated heat exchangers, pumps and thelike. In such a system, the pressure in the rst of the columns issufficiently high to permit condensation of the overhead propylene withcooling water while the bottoms also contains sufficient propylene(plus, of course, propylene oxide, ethylbenzene and alpha phenylethanol)to allow the bottoms temperature to remain within the hereinabovedescribed limits. Such a column typically contains l2 theoreticalvapor-liquid contacting stages and operates with a reflux ratio (mols ofreflux per mol of net liquid overhead product) of 0.8:1. Suitableoverhead temperatures and pressures are respecti-vely 55 C. and 355p.s.i.a. while the suitable bottoms temperatures and pressures arerespectively C. and 360 p.s.i.a.

The second column desirably operates at a lower pressure and is used toremove the balance of the propylene from the propyleneoxide-ethylbenzene-alpha phenylethanol. Suitable operatingcharacteristics for this second column would include an overheadtemperature and pressure of respectively -25 C. and 32 p.s.i.a. and abottoms temperature and pressure respectively of 130 C. and 37 p.s.i.a.Such a column suitably contains 15 theoretical vapor-liquid contactingstages and operates with 0.6 mols of liquid refiux per mol of feedentering the column. Because of the low overhead temperature, the secondcolumn requires vapor compression and/or refrigeration facilities topermit condensation of propylene. The bottoms from the second column insuch a system is an essentially propylene-free mixture comprisingpropylene oxide, ethylbenzene, and alpha phenylethanol.

EXAMPLE The following example is presented to further illustrate thisinvention but is not intended as limiting the scope thereof. Unlessotherwise stated, all parts and percents in this example are expressedon a molar basis.

Example 1 A continuous epoxidation experiment is conducted in apparatussimilar to that schematically depicted in FIG. l. Insofar as isnecessary for an understanding of the invention, details of theapparatus will be described in conjunction with the followingdescription of the epoxidation.

Ethylbenzene hydroperoxide plus ethylbenzene and alpha phenyl ethanolsolvent are fed to a reaction vessel at the rate of .5.86 parts perhour. Also present in this stream is molybdenum catalyst sufficient toprovide 75 p.p.m. (by weight) of molybdenum in the total reactor feed.Composition of this stream is given in the first column of Table I. Alsofed to this reactor are 15.81 parts per hour of propylene, of which 0.79parts per hour are fresh propylene and 15.02 parts per hour are recycledpropylene. The recycle propylene is distributed -between the variouscompartments in order to maintain the temperature constant. For the sakeof completeness in Table I, these stream compositions are included inthe second and third columns thereof.

The reactor in which the epoxidation reaction occurs is divided byinternal baffles into five compartments so sized that the totalresidence time of the liquid phase reaction medium within allcompartments is about 11 minutes. The baffles are so arranged that theliquid phase reaction medium flows sequentially from compartment tocompartment and is withdrawn after the fifth compartment of the reactor.Vapor space is also provided within each compartment and the vaporspaces of each compartment are not isolated from one another, i.e., theyare interconnected.

The epoxidation reactor is maintained at a temperature of 132 C. and ismaintained under autogenous pressure of the systemin this case 375p.s.i.a.

During the course of the reaction 11.21 parts per hour of the liquidphase reaction medium are vaporized and are withdrawn from the reactoras a vapor. The composition of this vapor is given in the fourth columnof Table I. Also, 10.46 parts per hour of liquid phase reaction mediumhaving the composition set forth in the fifth column of Table I arewithdrawn from the reactor.

The net vapors from the reactor are fractionated to recover unreactedpropylene for recycle and propylene oxide product in admixture withalpha phenyl ethanol and ethylbenzene as the product. This isaccomplished in conventional distillation equipment indicated as column30. Also processed in this distillation equipment is the liquid phasereaction medium withdrawn from the reactor as hereinabove described. Therecycle propylene amounts to 15.02 parts per hour and has thecomposition set forth in the sixth column of Table I. The bottomsproduct from this distillation amounts to 6.65 parts per hour and hasthe composition listed in the seventh column of Table I. During thisdistillation, the bottoms temperature is controlled so that it does notexceed about 130 C. The bottoms product from this distillation can thenbe processed in known manner so as to recover propylene oxide in highpurity in subsequent equipment eg., distillation equipment, in knownmanner.

It will be noted that the selectivity to propylene oxide based on totalhydroperoxide converted in the reactor in this example is 75 molpercent. In contrast, in a control experiment wherein the reactorpressure was maintained at a level above the autogenous pressure of thesystem, i.e., wherein no vaporization of the reaction medium takesplace, a significantly lower selectivity is obtained.

The foregoing description illustrates the methods of this inventionwhereby the advantages thereof are obtained. It will be understood thatmodifications and variations thereof may be etected by those skilled inthe art without departing from the spirit of our invention. For example,in a multi Zoned reactor the temperature can be the same in each zone orthe temperature can vary from zone to Zone. It is sometimes desirable tohave somewhat higher temperatures in the last zones to insure morecomplete reaction at the lower reactant concentrations. Also each zoneshould have adequate agitation. Suitable agitation can be achieved bythe boiling effect, by mechanical agitations, by appropriate sparging ofmaterials fed to the zones, by pump around procedures or by combinationsthereof. Accordingly, it is intended that all matter contained in theabove description shall be interpreted as illustrative and not in alimiting sense.

that the total residence time of the liquid phase reaction medium withinall compartments is 32 minutes based on the flow of liquid leaving thereactor in line 19. The baffles are so arranged that the liquid phasereaction medium ows sequentially from compartment to compartment and iswithdrawn after the fifth compartment of the reactor.

During the course of the reaction 28.3 parts per hour by weight ofliquid phase reaction medium are vaporized and are withdrawn from thereactor as a vapor through line 18. This vapor stream contains 0.64parts per hour of propylene oxide by weight. Also, 12.3 parts per hourby weight of liquid phase reaction medium are withdrawn from the reactorthrough line 19. This stream contains 1.10 parts per hour of propyleneoxide by weight.

Analyses of streams 18 and 19 show that 83% of the t-butyl hydroperoxidefed to the reactor has been converted. The resulting selectivity ofpropylene oxide based on total hydroperoxide converted in the reactor is88 mol percent.

Example 3 (Comparative) The experiment of Example 2 is repeated butunder conditions where no net propylene oxide is removed from thereactor in the vapor boilup streams.

The reactor differs from the arrangement in FIG. 1 in that the vaporboilup from each of the 5 compartments is separately condensed andreturned to the compartment from which the vapor evolved. Thus each ofthe 5 compartments are provided with a separate condenser. Bafes areprovided to separate the vapor spaces between compartments, and overfiowdevices are provided to permit liquid flow from compartment tocompartment in series. No net vapors are removed from the reactor. Thefeed is 10 parts per hour by weight of a 37 weight percent tbutylhydroperoxide solution containing 300 p.p.m. by weight of molybdenumcatalyst, This is the same feed as used in Example 2. The total feedrate of fresh plus recycle propylene from lines 13 and 36 is 6.6 partsper hour by weight. This propylene feed is distributed among the 5compartments to maintain a temperature of 121 C. and a pressure of 600p.s.i.a. in each compartment. The

TABLE I.-STREAM COMPOSITIONS FOR EXAMPLE I [Mol percent] n Excludescatalystl b Excludes inerts, ag., propane, ethane, n1trogen,earbondioxide, etc. High-boiling reaction by-produets.

d 75 p.p.m., molar.

5 ppm., molar.

Example 2 A continuous epoxidation experiment is conducted in apparatussimilar to that schematically depicted in FIG. 1 of the originaldisclosure.

T-butyl hydroperoxide plus t-butyl alcohol solvent are fed to a reactionvessel at the rate of 10.0 parts per hour by weight. This streamcontains 37 weight percent t-butyl hydroperoxide and also contains 300p.p.m. by weight of molybdenum catalyst. Also fed to this reactor are30.6 parts per hour by weight of fresh plus recycled propylene throughlines 36 and 13. The pressure in the reactor is maintained at 600p.s.i.a. by removal of vapor through line 18. The propylene feed isdistributed among the various compartments so that a temperature of 121C. is maintained in each compartment.

The reactor in which the epoxidation reaction occurs is divided byinternal baflies into 5 compartments so sized compartments are sized togive a residence time of 32 minutes based on ow of exit liquid throughline 19.

16.6 parts per hour by weight of liquid phase reaction medium arewithdrawn from the fifth compartment of the reactor. This is the onlynet process steam removed from the reactor. Analysis of this liquideffluent stream shows that it contains 1.63 parts per hour by weight ofpropylene oxide, and that 83% of the t-butyl hydroperoxide feed has beenconverted. The selectivity to propylene oxide based on totalhydroperoxide converted is 82.5 mol percent.

The superior propylene oxide selectivity obtained in Example 2 ascompared with Example 3 is believed to be the result of propylene oxideremoval from the reaction liquid in the exit vapor stream, therebypreventing the partial degradation of propylene oxide through reactionwith t-butyl hydroperoxide and with other trace constitu- 9 ents such asacids and water. It should be noted that the concentrations ofpropylene, molybdenum, and t-buty1 hydroperoxide in the liquid reactionmedium are essentially the same in Example 3 as in Example 2.

What is claimed is:

1. In the continuous process for the preparation of propylene oxide bythe reaction between propylene and an organic hydroperoxide in thepresence of a liquid phase reaction medium and in the presence of acatalyst selected from at least one member of the group consisting oftitanium, Vanadium, chromium, columbum, selenium, zirconium, molybdenum,tellurium, tantalum, tungsten, rhenium and uranium; the improvementwhich comprises, continuously conducting the reaction in a reactor at atemperature within the range between about 90 C. and about 200 C. and atthe autogenous pressure of the liquid phase reaction medium so that saidmedium is a boiling liquid, the reactor feed comprising 10 to 8O molpercent propylene and 1 to 60 mol percent hydroperoxide, continuouslyvolatilizing a portion of the liquid phase reaction medium during theconduct of the reaction, as a result of said boiling, said volatilizedportion containing at least one-fourth of the propylene oxide formed inthe reaction, withdrawing the propylene oxide containing va- 4dationreaction as part of the said feed thereto.

2. A process in accordance with claim 1 wherein the organichydroperoxide is ethylbenzene hydroperoxide.

3. A process in accordance with claim 1 wherein the reaction temperatureis between 90 C. and about 150 C.

References Cited UNITED STATES PATENTS 3,351,635 11/1967 Kollar260-348.5 3,526,645 9/ 1970 Vangermain et al, 260-348.5 2,644,837 7/1953 Schweitzer 260--484 1,916,473 7/ 1933 Forrest et al.

FOREIGN PATENTS 1,421,285 11/ 1965 France 260-348.5

porized reaction medium from the reactor as a vapor, 25 NORMA S.MILESTONE, Primary Examiner

1. IN THE CONTINUOUS PROCESS FOR THE PREPARATION OF PROPLENE OXIDE BY THE REACTION BETWEEN PROPYLENE AND AN ORGANIC HYDROPEROXIIDE IN THE PRESENCE OF A LIQUID PHASE REACTION MEDIUM AND IN THE PRESENCE OF A CATALYST SELECTED FROM AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF TITANIUM, VANADIUM, CHROMIUM, COLUMBIUM, SELENIUM, ZIRCONIUM, MOLYBDENUM, TELLURIUM, TANTALUM, TUNGSTEN, RHENIUM AND URANIUM; THE IMPROVEMENT WHICH COMPRISES, CONTINUOUSLY CONDUCTING THE REACTION IN A REACTOR AT A TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 90* C. AND ABOUT 200* C. AND AT THE AUTOGENOUS PRESSURE OF THE LIQUID PHASE REACTION MEDIUM SO THAT SAID MEDIUM IS A BOILING LIQUID, THE REACTOR FEED COMPRISING 10 TO 80 MOL PERCENT PROPYLENE AND 1 TO 60 MOL PERCENT HYDROPEROXIDE, CONTINUOUSLY VOLATILIZING A PORTION OF THE LIQUID PHASE REACTION MEDIUM DURING THE CONDUCT OF THE REACTION, AS A RESULT OF SAID BOILING, SAID VOLATILIZED PORTION CONTAINING AT LEAST ONE-FOURTH OF THE PROPYLENE OXIDE CONTAINING VA , REACTION, WITHDRAWING THE PROPYLENE OXIDE CONTAINING VAPROIZED REACTION MEDIUM FROM THE REACTOR AS A VAPOT, CONTINUOUSLY WITHDRAWING THE UNVAPORIZED REACTION MEDIUM CONTAINING THE BALANCE OF THE PROPYLENE OXIDE PRODUCT FROM THE REACTOR AS A LIQUID, CONTINUOUSLY SEPARATING PROLYLENE OXIDE FROM SAID WITHDRAWING VAPORIZED REACTION MEDIUM BY FRACTIONAL DISTILLATION AT TEMPERATURES NOR TO EXCEED 160* C. AND CONTINUOUSLY RECYCLING PROPYLENE IN SAID WITHDRAWN VAPORIZED REACTION MEDIUN TO THE EPOXIDATION REACTION AS PART OF THIS FEED THERETO. 